The present invention relates to a novel process for preparing arylaminohydroxyanthraquinones.
The condensation of arylamines with chlorohydroxyanthraquinones is well known; see NL-A-6 504 570 and GB-A-1 527 383. However, these processes have serious disadvantages.
NL-A-6 504 570 utilizes the arylamine in high excess and hence also as solvent. This leads to high amine contents of above 1% in the dye, so that for many applications (coloration of children""s toys, food packaging, etc) it is absolutely necessary to redissolve the dye in another solvent. Furthermore, the dye quality obtained does not meet present-day requirements with regard to brilliance. In GB-A-1 527 383, arylaminohydroxyanthraquinones are prepared from chlorohydroxyanthraquinones and arylamines in an inert solvent (eg ethoxyethanol) using boric acid and an excess of arylamine as base. The dye obtained from this process likewise is not of adequate quality and would have to be subjected to further purification steps, for example a recrystallization.
There has now been found a process whereby arylaminohydroxyanthraquinones can be prepared in very good yields and in high purity without the abovementioned disadvantages.
The present invention accordingly provides a process for preparing arylaminohydroxyanthraquinones of the formula (I) 
where
R1, R2, R3 and R4 are independently hydrogen, hydroxyl or NHxe2x80x94Ar, where
Ar is an aryl radical optionally substituted by one or more, identical or different substituents,
xe2x80x83with the proviso that at least one of R1 to R4 is OH and at least one of R1 to R4 is xe2x80x94NHxe2x80x94Ar,
by reacting appropriate chlorohydroxyanthraquinones of the formula (II) 
xe2x80x83where
R5, R6, R7 and R8 are independently hydrogen, chlorine or hydroxyl,
with the proviso that at least one of R5 to R8 is chlorine and at least one of R5 to R8 is hydroxyl,
with an amine of the formula (III)
H2Nxe2x80x94Arxe2x80x83xe2x80x83(III),
xe2x80x83where
Ar is as defined above,
characterized in that one mole of amine of the formula (III) plus an excess of 10 to 100% based on one mole of amine is used per chlorine atom in the compounds of the formula (II) and the reaction is carried out in an inert solvent in the presence of a base selected from the group consisting of the carbonates of the alkali and alkaline earth metals, the acetates of the alkali metals, the phosphates of the alkali metals and any mixtures thereof.
The compounds of the formula (II) are preferably 1-chloro-4-hydroxyanthraquinone, 4,8-dichloro-1,5-dhydroxyanthraquinone, 4,5-dichloro-1,8-dihydroxyanthraquinone, 8-chloro-1,4,5-trihydroxyanthraquinone or 5,8-dichloro-1,4-dihydroxyanthraquinone.
The aforementioned chlorohydroxyanthraquinones of the formula (II) are generally used in pure form for the process of the invention. However, it is also possible, with similar success, to use the compounds (II) in the form of technical-grade material.
This technical-grade material, as well as compounds of the formula (II), will then generally additionally contain 15 to 25% of impurities in the form of more highly substituted products and/or products which are isomeric to the formula (II).
The process of the invention is preferably carried out using 5,8-dichloro-1,4-dihydroxyanthraquinone in the form of technical-grade material. The chlorine atoms in the by-products present in the technical-grade material will likewise be replaced by amino groups in the course of the reaction with the amine (III) according to the invention. These reaction products, however, remain in the mother liquor and can be removed with the mother liquor from the products (I) prepared according to the invention and thus do not constitute an impairment to the quality of the end product.
More particularly, Ar is naphthyl optionally substituted by one or more identical or different substituents selected from the group consisting of alkyl and halogen or is phenyl optionally substituted by one or more identical or different substituents selected from the group consisting of cyano, carboxyl, nitro, alkylsulphonyl, carbonyl, sulfo, alkylaminocarbonyl, alkylcarbonylamino, alkyl, cycloalkyl, alkoxy, trifluoromethyl, halogen and aryl, which in turn may be substituted by the radicals mentioned above for naphthyl and phenyl.
Alkyl, alone or as part of compound terms such as alkylsulphonyl, alkylaminocarbonyl and alkylcarbonylamine, is especially straight-chain or branched C1 to C6-alkyl. Cycloalkyl is especially cyclopentyl or cyclohexyl. Alkoxy is preferably straight-chain or branched C1- to C6-alkoxy. Aryl is especially phenyl or naphthyl. Halogen is preferably chlorine or bromine.
Preferred substituents for phenyl and naphthyl are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, cyclohexyl, methoxy, chlorine, bromine and phenyl, which may in turn be substituted. Particular preference is given to methyl, tert-butyl, n-butyl, cyclohexyl and phenyl.
The arylamines (III) are used in the theoretically required amount plus an excess of preferably 10 to 50%, particularly preferably 10 to 30%, especially preferably 10 to 20%, based on 1 mol of arylamine.
Preferred inert solvents are:
N-methylpyrrolidone, chlorobenzene, 1,2-dichlorobenzene, 1,2,4-trichlorobenzene, xylene, nitrobenzene and phenol.
Particular preference is given to N-methylpyrrolidone and dichlorobenzene.
Preferred bases are sodium carbonate, potassium carbonate, sodium acetate, potassium acetate, trisodium phosphate, disodium hydrogenphosphate and sodium dihydrogenphosphate or mixtures of the carbonates with acetates and mixtures of the carbonates with the phosphates.
Particular preference is given to disodium hydrogenphosphate, trisodium phosphate and mixtures of sodium carbonate with sodium acetate. The amount of base used is generally from 0.5 to 2.5 equivalents of base, preferably 0.5 to 1 equivalent, per chlorine atom to be replaced in the compounds of the formula (II) or per mole of hydrochloric acid released.
The reaction is carried out at a temperature between 80xc2x0 and 200xc2x0 C., preferably between 110xc2x0 and 190xc2x0 C.
The impurities remain dissolved in the mother liquor and are virtually completely removed in the course of isolation by filtration and washing of the residue by displacement of the mother liquor.
The process of the invention provides the arylaminohydroxyanthraquinones in very good yield of 80 to 100%, preferably  greater than 90%, with the level of impurities due to amine (III) being less than 600 ppm, preferably less than 300 ppm.
The compounds of the formula (I) are useful dyes for the transparent and hiding coloration of plastics such as polystyrene, polyamide, polycarbonate, polyethylene, polyester, eg polyethylene terephthalate or polyethylene butylate, ABS and ABS-PC blends. They are used not only for mass coloration but also for spin dyeing.